Long-chain omega-3 polyunsaturated fatty acids are essential fatty acids for humans and must be supplied by the diet. Of these, docosahexaenoic acid, C22:6 Δ4,7,10,13,16,19 (DHA) has particular health benefits, and is used not only as a food supplement but also as a pharmaceutical compound for treatment of coronary diseases (Wynn et al, 2005).
DHA is a superior polyenoic acid, as this can easily be converted to other essential polyenoic fatty acids like eicosapentaenoic acid (EPA). Conversion of EPA to DHA is not possible in the human body.
For enrichment of oils to be used in functional foods, and for pharmaceutical applications, there is a need for concentrates of fatty acids or their alkyl ester derivatives. Currently, compositions containing polyunsaturated fatty acids are obtained from fish oils. However, there is a concern that sufficient fish oil will not be available in the future (Lewis et al., 1999). Moreover, reports of the possible accumulation of toxic pollutants, including heavy metals, dioxins and polychlorinated biphenyls (PCBs) from the marine environment into fish lipids, have imposed the needs for extensive purification processes for fish oils intended for human consumption and animal feed (Ratledge, 2004).
An alternative to fish oil is microbial sources. Some marine, heterotrophic microalgae accumulate large quantities of DHA, such as Crypthecodinium cohnii (e.g. U.S. Pat. No. 5,407,957) and thraustochytrids (e.g. WO Patent No. 9408467; U.S. Pat. No. 6,509,178). These microorganisms often accumulate more than 50% of their dry weight as lipids, with DHA frequently constituting more than 25% of total lipids (Lewis et al., 1999; Yokochi et al., 1998; Yaguchi et al., 1997). An additional advantage of microbial production of DHA, compared to fish oils, is that DHA is the only, or dominating, long-chain PolyUnsaturated Fatty Acid (PUFA), making the purification process simpler.
Conventionally, marine and vegetable oils are isolated from the biomass by thermal-mechanical processes and/or solvent extraction. When fatty acid alkyl esters are the desired product, the extracted oil is transesterified, often in the presence of a catalyst. In general, the conventional way of obtaining fatty acids from microalgae or fish includes several steps that might be detrimental to the fatty acids, particularly the unstable polyunsaturated fatty acids. The fatty acids are subjected to extensive and tough handling, and high temperature.
Thus, there is a need for new processes for the extraction of fatty acids, particularly LC-PUFA to meet the growing market and the demand for high quality polyunsaturated fatty acids, especially DHA.